From the very beginning of the art of confining fluids, and particularly gases under pressure, there has been the necessity of providing a pressure relief device which would open when the internal pressure exceeded some predetermined amount. Originally, this type of device usually consisted of a conical plug mounted on a lever arm at the outer end of which was a weight suitably adjusted to control the pressure within the chamber, i.e., the old "steam engine" safety valve. More recently, these have usually comprised a metal disc placed in a body threaded into the container, the metal being adapted to rupture to release excessive pressure. Such devices have three objections:
1. They are of excessive size when desired for use with small devices, whereby the pressure relief device was out of proportion, both as to size and as to cost of small pressure-fluid containers; PA1 2. the devices operate only at high pressures, such as 100 pounds per square inch for a 1/2-inch device; 500 pounds psi for a 1/4-inch device; 1,000 pounds psi for a 1/8-inch device, etc; PA1 3. the devices are extremely costly.
The pressure relief device of the present invention can be made smaller and less expensively, and can be adapted to pressures of from 5 to 10,000 pounds per square inch. The fluid pressure relief device of the present invention does not rely upon rupture of the material but upon its deformation to permit slippage of the sealing element within the body of the device. In the preferred form, the inner bore of the body is flared outwardly at its inner end and the plug of a corresponding or a slightly greater flare to fit snugly within the flare of the bore in the body. Since the material is deformable, at a particular pressure the seal will be pushed outwardly in the bore of the body, past a pressure relief port. The pressure at which the device is to operate can be predetermined over a wide range of values. For example, in one device having a 3/16 inch bore, I was able to consistently operate the device at predetermined pressures between 440 pounds per square inch and 4,400 pounds per square inch when using solder as the plug, the variation being accomplished by the depth to which it was inserted in the bore of the body. Likewise, the pressure at which the solder plug will operate can be widely varied by varying the thickness of the plug walls. With the same body, and using "Teflon" for the plug, I was able to consistently operate the pressure relief device at pressures of 130 psi down to as low as 13 psi, again depending upon the depth of the insertion of the plug in the bore of the body. Again, the pressure at which the device operates can be easily controlled by changing the thickness of the wall, and particularly the flaring skirt, of the "Teflon" plug. By use of other materials for the plug and modifications in the shape of the plug and thickness of its walls, the pressure at which the device operates can be brought down to 5 psi, or even less, or increased to 10,000 psi, or more.